Soldering a conductor to an aluminum metallization

ABSTRACT

A method of making a semiconductor including soldering a conductor to an aluminum metallization is disclosed. In one example, the method includes substituting an aluminum oxide layer on the aluminum metallization by a substitute metal oxide layer or a substitute metal alloy oxide layer. Then, substitute metal oxides in the substitute metal oxide layer or the substitute metal alloy oxide layer are at least partly reduced. The conductor is soldered to the aluminum metallization using a solder material.

CROSS-REFERENCE TO RELATED APPLICATION

This Utility Patent Application is a continuation application of U.S.Ser. No. 16/036,252 filed Jul. 16, 2018 and claims priority to GermanPatent Application No. 10 2017 213 170.5, filed Jul. 31, 2017, which isincorporated herein by reference.

TECHNICAL FIELD

This disclosure relates generally to the technique of soldering insemiconductor device manufacturing, and in particular to aspects ofsoldering a conductor to an aluminum metallization.

BACKGROUND

Soldering processes are widely used in semiconductor devicemanufacturing for a variety of purposes, including chip bonding,wire/clip/ribbon bonding, device mounting etc. A variety of soldermaterials, fluxes, and soldering techniques is available. Solderingmethods and soldering substances can have a high impact on cost, yield,performance and reliability of a semiconductor device.

Soldering of aluminum (Al) metallizations requires the application ofhighly reactive chemicals (fluxes) to remove the highly stable Al₂O₃layer on Al metallizations. Such highly reactive chemicals areincompatible with standard semiconductor manufacturing processes.Therefore, soldering on Al surfaces today is limited to applicationsoutside of semiconductor device manufacturing.

SUMMARY

An aspect of the disclosure relates to a method of soldering a conductorto an aluminum metallization. The method includes substituting analuminum oxide layer on the aluminum metallization by a substitute metaloxide layer or a substitute metal alloy oxide layer. A substitute metaloxide in the substitute metal oxide layer or the substitute metal alloyoxide layer is at least partly reduced. The conductor is soldered to thealuminum metallization using a solder material.

Another aspect of the disclosure relates to a method of soldering aconductor to an aluminum metallization. The method includes applying aflux material to an aluminum oxide layer on the aluminum metallization.A solder material is disposed over the aluminum metallization, whereinthe solder material has a chemical composition in percent by weight (%wt) of x % wt≤Zn≤100% wt, with x=10, 30, 50, 70, 90, 95, or 100. Theconductor is then soldered to the aluminum metallization.

Another aspect of the disclosure relates to a method of soldering aconductor to an aluminum metallization. The method includes applying ahalogenide via a plasma process to an aluminum oxide layer on thealuminum metallization to produce a halogenated aluminum oxide layer. Asolder material is disposed over the halogenated aluminum oxide layer.The conductor is then soldered to the aluminum metallization.

Another aspect of the disclosure relates to an arrangement of aconductor and an aluminum metallization soldered together. Thearrangement includes a substitute metal layer or a substitute metalalloy layer disposed over the aluminum metallization, wherein asubstitute metal of the substitute metal layer or the substitute metalalloy layer may be one of Zn, Cr, Cu, Pb, or Sn. The arrangement furtherincludes a solder layer arranged between the substitute metal layer orthe substitute metal alloy layer and the conductor.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of aspects and are incorporated in and constitute a partof this specification. The drawings illustrate aspects of the disclosureand together with the description serve to explain principles of aspectsof the disclosure. Other aspects and many of the intended advantages ofaspects will be readily appreciated as they become better understood byreference to the following detailed description. The elements of thedrawings are not necessarily to scale relative to each other. Likereference signs may designate corresponding similar parts. It is to beunderstood that the features of the various examples of embodimentsdescribed below may be combined with each other, unless specificallynoted otherwise.

FIG. 1A is a cross-sectional view illustrating an example of an aluminummetallization and an aluminum oxide layer on the aluminum metallization.

FIG. 1B is a cross-sectional view illustrating exemplary activationprocesses of the aluminum oxide layer of FIG. 1A.

FIG. 1C is a cross-sectional view illustrating exemplary substitutionprocesses of the aluminum oxide layer of FIG. 1A or FIG. 1B by asubstitute metal oxide layer or a substitute metal alloy oxide layer.

FIG. 1D is a cross-sectional view illustrating exemplary reduction ofthe substitute metal oxide layer or the substitute metal alloy oxidelayer of FIG. 1C.

FIG. 1E is a cross-sectional view illustrating the aluminummetallization after the reduction process of FIG. 1D.

FIG. 1F is a cross-sectional view illustrating exemplary application ofa solder deposit over the aluminum metallization of FIG. 1E.

FIG. 1G is a cross-sectional view illustrating exemplary placement of aconductor onto the solder deposit of FIG. 1F.

FIG. 1H is a cross-sectional view illustrating exemplary soldering andcooling of the conductor placed onto the solder deposit according toFIG. 1G.

FIG. 1I is a cross-sectional view illustrating an example of a conductorsoldered to an aluminum metallization by exemplary processes asillustrated, e.g., in FIGS. 1A to 1H.

FIG. 2 is a diagram illustrating calculated equilibrium pressures p inunits of Pa of H₂O for the metal oxides Al₂O₃, Cr₂O₃, and ZnO in areducing gas of 5% H₂ in N₂ (forming gas) and for the metal oxide Al₂O₃in a reducing gas of CH₂O₂ in N₂ versus temperature T in units of K.

FIG. 3A is a cross-sectional view illustrating an exemplary applicationof a solder deposit over the aluminum metallization of FIG. 1C.

FIG. 3B is a cross-sectional view illustrating exemplary placement of aconductor onto the solder deposit of FIG. 3A.

FIG. 3C is a cross-sectional view illustrating exemplary soldering andcooling of the conductor placed onto the solder deposit according toFIG. 3B.

FIG. 3D is a cross-sectional view illustrating an example of a conductorsoldered to an aluminum metallization by exemplary processes asillustrated, e.g., in FIGS. 1A to 1C followed by exemplary processes asillustrated, e.g., in FIGS. 3A to 3C.

FIG. 4A is a cross-sectional view illustrating an exemplary applicationof a solder paste over the aluminum metallization of FIG. 1A.

FIG. 4B is a cross-sectional view illustrating exemplary placement of aconductor onto the solder paste of FIG. 4A.

FIG. 4C is a cross-sectional view illustrating exemplary soldering andcooling of the conductor placed onto the solder paste according to FIG.4B.

FIG. 4D is a cross-sectional view illustrating an example of a conductorsoldered to an aluminum metallization by exemplary processes asillustrated, e.g., in FIG. 1A, followed by exemplary processes asillustrated, e.g., in FIGS. 4A to 4C.

FIG. 5A is a cross-sectional view illustrating an example of an aluminummetallization and an aluminum oxide layer on the aluminum metallization.

FIG. 5B is a cross-sectional view illustrating exemplary activationprocesses of the aluminum oxide layer of FIG. 1A.

FIG. 5C is a cross-sectional view illustrating exemplary application ofa solder deposit over the aluminum metallization of FIG. 5B.

FIG. 5D is a cross-sectional view illustrating exemplary placement of aconductor onto the solder deposit of FIG. 5C.

FIG. 5E is a cross-sectional view illustrating exemplary soldering andcooling of the conductor placed onto the solder deposit according toFIG. 5D.

FIG. 5F is a cross-sectional view illustrating an example of a conductorsoldered to an aluminum metallization by exemplary processes asillustrated, e.g., in FIGS. 5A to 5E.

FIG. 6 is a cross-sectional view illustrating an exemplary arrangementof a conductor and an aluminum metallization soldered together, whereinthe conductor is a chip carrier or a clip and the aluminum metallizationis a chip electrode.

FIG. 7 is a cross-sectional view illustrating an exemplary arrangementof a conductor and an aluminum metallization soldered together, whereinthe conductor is a chip electrode and the aluminum metallization is achip carrier or a clip.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings, which form a part thereof, and in which is shownby way of illustration specific embodiments. In this regard, directionalterminology, such as “top”, “bottom”, “front”, “back”, “upper”, “lower”,etc., is used with reference to the orientation of the Figure(s) beingdescribed. Because components of embodiments can be positioned in anumber of different orientations, the directional terminology is usedfor purposes of illustration and is in no way limiting. It is to beunderstood that other embodiments may be utilized and structural orlogical changes may be made without departing from the scope of thepresent description. The following detailed description, therefore, isnot to be taken in a limiting sense.

As employed in this specification, the terms “bonded”, “attached”,“connected”, “coupled” and/or “electrically connected/electricallycoupled” are not meant to mean that the elements or layers must directlybe contacted together; intervening elements or layers may be providedbetween the “bonded”, “attached”, “connected”, “coupled” and/or“electrically connected/electrically coupled” elements, respectively.However, in accordance with the disclosure, the above-mentioned termsmay, optionally, also have the specific meaning that the elements orlayers are directly contacted together, i.e. that no interveningelements or layers are provided between the “bonded”, “attached”,“connected”, “coupled” and/or “electrically connected/electricallycoupled” elements, respectively.

Further, the word “over” used with regard to a part, element or materiallayer formed or located “over” a surface may be used herein tooptionally mean that the part, element or material layer be located(e.g. placed, formed, deposited, etc.) “directly on”, e.g. in directcontact with, the implied surface. The word “over” used with regard to apart, element or material layer formed or located “over” a surface maybe used herein to mean that the part, element or material layer belocated (e.g. placed, formed, deposited, etc.) “indirectly on” theimplied surface with one or more additional parts, elements or layersbeing arranged between the implied surface and the part, element ormaterial layer.

Further, geometric terminology such as the words “perpendicular” and“parallel” etc. may be used herein with regard to a relative orientationof two or more components. It is understood that these terms may notnecessarily mean that the specified geometric relation is realized in aperfect geometric sense. Instead, fabrication tolerances of the involvedcomponents may need to be considered in this regard. For example, if twosurfaces of an encapsulation material of a semiconductor package arespecified to be perpendicular (or parallel) to each other, an actualangle between these surfaces may deviate from an exact value of 90 (or0) degrees by a deviation value that may particularly depend ontolerances that may typically occur when applying techniques forfabricating a housing made of the encapsulation material.

Further, an “alloy of X” (including further components Y, Z, . . . )means that the contribution of X in % wt is greater than thecontribution of Y in % wt and the contribution of Z in % wt,respectively. In particular, it may mean that the contribution of X isat least 50% wt.

The notation XY refers to an alloy of X including at least Y as afurther component. In particular, it may refer to an alloy of Xincluding Y as a sole residual component.

Embodiments of methods described herein may be used for solderingsemiconductor devices such as, e.g., semiconductor chips, havingelectrically conducting electrodes to an aluminum substrate. Further,embodiments of methods described herein may be used for solderingsemiconductor device aluminum metallization such as, e.g., chip aluminumelectrodes to a metal substrate, wherein the metal substrate maycomprise or be made of, e.g., copper, a copper alloy, aluminum, analuminum alloy, etc.

As known in the art, an aluminum metallization is coated by a highlystable Al₂O₃ layer. Al₂O₃ has a free enthalpy of formation ofDGf⁰=−1582.3 kJ/mol. This highly stable oxide protects the aluminum fromsolder attack with solderpastes containing fluxes which are usually usedin semiconductor soldering, such as low activated fluxes based onkolophonium or other organic acids such as malonic acid or oxalic acid.The highly stable Al₂O₃ layer may be removed by highly reactivechemicals such as, e.g., HCl or HF mixed with H₂SO₄. However, thesehighly reactive chemicals cannot be applied in semiconductor processing.

Further, a bare aluminum surface is only stable for a short period oftime because of the high forming rate of Al₂O₃ on bare aluminum. Thisconventionally requires in addition the usage of highly activatingfluxes or specific salt mixtures that carry chloride and fluoride ions.The involvement of such species, however, imposes a high corrosion riskin semiconductor devices and is therefore not yet considered possible insemiconductor applications.

FIGS. 1A to 1I illustrate stages of various embodiments of a method ofsoldering a conductor to an aluminum metallization according to a firstaspect of the disclosure. Referring to FIG. 1A, an aluminummetallization 110 is covered by an aluminum oxide layer 120. Thealuminum oxide layer 120 may comprise or be of Al₂O₃. As mentionedabove, the aluminum metallization 110 may, e.g., be a semiconductor chipelectrode or a substrate or chip carrier such as, e.g., a leadframe, ora metallization on a substrate or chip carrier such as, e.g., ametallization on a PCB (printed circuit board) or a metallization on aceramic substrate.

Furthermore, it is to be noted that the aluminum metallization 110 doesnot need to be of aluminum only but may be an aluminum alloy, i.e. maycontain contributions of, e.g., Si and/or Cu and/or Mg and/or SiCuand/or other elements. For instance, the aluminum metallization 110 maybe an AlSiCu alloy containing, e.g., 0% wt≤Cu≤5% wt and 0% wt≤Si≤1% wt.By way of example, the aluminum metallization 110 may be a 98.5Al-1Si-0.5Cu (i.e. 98.5% wt of Al, 1% wt of Si, 0.5% wt of Cu) aluminumalloy. Such aluminum alloys, in particular AlMg, AlSi, AlCu, or AlSiCu,will also be referred herein as an “aluminum metallization”.

The aluminum oxide layer 120 may have a thickness of several nm, e.g. athickness of up to 2 nm or a thickness of up to 5 nm. An aluminum oxidelayer 120 of such thickness forms a very stable passivation layer whichcannot be removed easily via a conventional acidic treatment.

In the following, several possibilities are disclosed how to substitutethe Al₂O₃ layer with a less stable metal oxide or metal alloy oxidewithout a corrosive impact to the semiconductor device (e.g.semiconductor chip).

According to several embodiments, the process of substituting thealuminum oxide layer on the aluminum metallization by a substitute metalor substitute metal alloy oxide layer may comprise activation. FIG. 1Bschematically illustrates several examples for activating the aluminumoxide layer 120. Activating the aluminum oxide layer 120 may have themeaning of decreasing the stability of the aluminum oxide layer 120. Inparticular, activating the aluminum oxide layer 120 may have the meaningof removing partly or completely the aluminum oxide which has beenformed previously. The process of activating the aluminum oxide layer120 is an optional process which can be omitted in several embodiments.

A possibility of activating the aluminum oxide layer 120 may compriseapplying one or more of HF (hydrofluoric acid) and MSA (methanesulfonicacid) to the aluminum oxide layer 120. By way of example, pure MSA or amixture of HF and MSA may be applied. The application of HF and/or MSAis indicated by arrows Ac. By way of example, a mixture of HF and MSA inan aqueous solution may be directly disposed on an upper (exposed)surface 120 a of the aluminum oxide layer 120. Fluoride ions may formcomplexes with the aluminum oxide layer 120 at the upper surface 120 aand may finally also form AlF₃ which can be dissolved later in an acidicsolution. The dissolution of the Al₂O₃ with HF and/or MSA decreases thestability of the aluminum (Al₂O₃) layer 120.

A further possibility of (optionally) activating the aluminum oxidelayer 120 for decreasing its stability includes the application offluorine via a RF (radio frequency) plasma process to the aluminum oxidelayer 120. A mixture of Ar and CF₄ gas may be used in the plasmaprocess. During this process fluorine is incorporated into the aluminumoxide layer 120. More specifically, the aluminum oxide layer 120 mayform AlF₃ during the plasma process. As mentioned above, the fluorinatedaluminum oxide layer 120 has a decreased stability and may, e.g., bedissolved later.

The above concept of applying fluorine for (optionally) activating thealuminum oxide layer 120 for decreasing its stability may be generalizedto the concept of incorporation of halogenides, e.g. one or more of F,Cl, Br, and J to activate the aluminum oxide layer 120 by weakening thealuminum oxide layer 120.

Several possibilities are available and may, e.g., be combined ifdesired:

(1) Plasma treatment of Al₂O₃ with fluorocarbon containing plasmas suchas, e.g., CHF₃, C₂F₂, CH₃F or CF₄ gases or gas mixtures, e.g. also mixedwith one or more of Ar, He, O₂, H₂ or H₂O. Again, F may be substitutedby other halogenides.

(2) Plasma treatment of Al₂O₃ with other fluorine or chlorine compoundplasmas such as, e.g., SF₆, CHCl₃, CH₂Cl₂, CH₃Cl, CCl₃.

(3) Plasma treatment of Al₂O₃ with brominated or iodized organicmolecules that leads to incorporation of these halogens into the Al₂O₃layer leading to a weakening of this layer.

During the plasma treatment of the Al₂O₃ with a halogenide-based plasmaa specific mixture of aluminum-oxyfluorides are forming which are lessstable and can be soldered with standard flux-solderpastes or even asolderwire in conditions described further below. Usual contents ofhalogenides (e.g. fluorine-based) in the Al₂O₃ layer may be measuredwith Auger depth profiles. Taking fluorine as an example, a F/O atomicconcentration ratio of, e.g., about 0.5 is observed at the F maximumpeak over sputter time. Atomic concentration ratios at the maximum Fcontent (or, in general, halogens content) along the Al₂O₃ layerthickness between 0.01 and 10 have been observed and may be suitable forsoldering of aluminum due to the weakened Al₂O₃ layer. As will beexplained further below, the treatment (activation) of the Al₂O₃ with ahalogenide-based plasma can also be used as a “stand alone” processwhere the Al₂O₃ with the incorporated halogen is directly soldered.“Stand alone” here means that no conversion of the Al₂O₃ layer by aprocess of substituting the aluminum by another metal or metal alloy maybe needed in this case.

All these approaches for activating the aluminum oxide layer 120 (i.e.the application of HF/MSA in an aqueous solution, the application of anAr/CF₄ gas mixture during an RF plasma process and the incorporation ofhalogens or halogenides into the aluminum oxide layer 120) may becombined. Further, additional processes of pre-treating the aluminummetallization 110 to weaken the stability of the aluminum oxide layer120 thereon may be added.

Referring to FIG. 1C, the (e.g. activated) aluminum oxide layer 120 isthen replaced by a substitute metal oxide layer 130 or substitute metalalloy oxide layer 130. This substitute layer will be referred herein asthe substitute metal or substitute metal alloy oxide layer 130.

The substitute metal which is used to form the substitute metal orsubstitute metal alloy oxide layer 130 may, e.g., be Zn, Cr, Cu, Pb, orSn. These metals may be used to substitute Al₂O₃ with lower freeenthalpy of formation. By way of example, the enthalpy of formation DGf⁰of some substitute metal oxides are given in the following table.

metal oxide DGf⁰ [kJ/mol] ZnO 300 CuO 146 Cu₂O 129.7 PbO 189.93 PbO₂217.33 SnO 256.9 SnO₂ 438.2These metal oxides can be dissolved from low activated fluxes and can bereduced into their metallic state during soldering in reductiveatmosphere.

In particular, when a substitute metal alloy oxide layer of Zn or Cr isformed, the substitute metal alloy may include at least two of theelements Zn, Cr, V, and Mo. More specifically, the substitute metal orsubstitute metal alloy may consist of one of Zn, Cr, ZnCr, CrZn, andalloys thereof including one or more of V and Mo.

The substituting may comprise depositing the substitute metal orsubstitute metal alloy over the (e.g. previously activated) aluminumoxide layer 120. According to a first possibility, an electrochemicaldeposition process may be used. This electrochemical deposition processmay include the usage of an electrochemical cell which includes acathode, an anode and a compartment for the electrolyte between theelectrodes. By way of example, an alkaline electrolyte may be used.

In the following, without loss of generality, Zn will be used as anexample of the substitute metal. However, the disclosure hereinanalogously encompasses other metals or metal alloys such as, e.g., Cras an example of a substitute metal.

For example, a bare Zn layer may be deposited over the (e.g. previouslyactivated) aluminum oxide layer 120. Alkaline electrolytes, which may beused, are, e.g., Zn(OH)₄ ²⁻ with cyanide or without cyanide.Alternatively, acidic or neutral electrolytes such as, e.g., ZnSO₄ orZnCl₂ based electrolytes, ZnSO₄ with NH₄, ZnSO₄ without NH₄, Zn²⁺ withNH₄Cl etc., may also be used to apply a bare Zn layer.

These or other bare Zn-based electrolytes may also include additivessuch as, e.g., chromate (Cr) and/or vanadate (V) and/or molybdate (Mo).In these cases, a ZnCr and/or ZnV and/or ZnMo metal alloy layer may bedeposited as substitute metal alloy over the aluminum oxide layer 120 byelectrochemical deposition. For ZnCr and/or ZnV and/or ZnMo alloy layerdeposition, also an alkaline electrolyte can be used. In this case, thealkaline electrolyte contains Cr ions and/or V ions and/or Mo ions andmay show anomalous co-deposition behavior of Cr and/or V and/or Motogether with Zn. The Cr and/or V and/or Mo content of the ZnCr and/orZnV and/or ZnMo alloy layer may be equal to or higher than 1% wt, inparticular 5% wt, and may be equal to or less than 40% wt, with the restis Zn and, optionally, minor contributions of other elements such as,e.g., Si, etc.

By way of example, for the deposition of a ZnCr alloy layer anelectrolyte including or consisting of 12 g/L NaOH, 0.9 g/L Zn²⁺, 0.6g/L Cr⁶⁺ and, optionally, 70 ppmSi⁴⁺ may be used. The ZnCr alloy layermay contain hexavalent Cr.

The Zn metal layer or the ZnCr and/or ZnV and/or ZnMo metal alloy layermay have a thickness of equal to or greater than 1, 5, 10, 20, 40, 60,or 80 nm. The Zn metal layer or the ZnCr and/or ZnV and/or ZnMo metalalloy layer may have a thickness of equal to or less than 100, 80, 40,20, 10, or 5 nm.

A second possibility of depositing the substitute metal or substitutemetal alloy over the aluminum oxide layer 120 is to use an electrolessdeposition process. An electroless deposition process may comprise achemical exposure of the upper surface 120 a of the aluminum oxide layer120 to an electrolyte without the application of a current. By way ofexample, all of the above-mentioned electrolytes may be used, and it ispossible to apply all substitute metal or substitute metal alloys (e.g.bare Zn or ZnCr, ZnV, ZnMo alloys) which are mentioned above. Thechemical exposure may be obtained by, e.g., a dip process of thealuminum metallization 110 in the electrolyte cell. By way of example,the aluminum metallization 110 (together with the aluminum oxide layer120 thereon) may be dipped into the electrolyte for about 15 to 60seconds.

All the exemplary processes described above result in a substitution ofthe aluminum oxide layer 120 by a substitute metal or substitute metalalloy oxide layer 130. With the substitution of the Al₂O₃ layer 120 bydeposition of a Zn or ZnCr or ZnV or ZnMo layer, the oxides ZnO,ZnCr-oxide, ZnV-oxide or ZnMo-oxide, respectively, are formed. Withthese new oxides formed and the Al₂O₃ vanished, the layer replacing thealuminum oxide layer 120 (i.e. the substitute metal or substitute metalalloy oxide layer 130) can more easily be reduced during subsequentprocessing since ZnO or the ZnCr—/ZnV—/ZnMo-oxides are thermodynamicallyless stable compared to Al₂O₃. As will be described in more detailfurther below, this reduction in stability may facilitate or alreadyallow subsequent soldering on the aluminum metallization 110.

It is to be noted that the substitution of the aluminum oxide layer 120by the substitute metal or substitute metal alloy oxide layer 130 isaccompanied by a structural and morphologic change of the layer. Morespecifically, the substitute metal or substitute metal alloy oxide layer130 may have a sponge-like, porous, dendritic or otherwise inhomogeneousstructure.

In the following, some specific examples are described for thesubstitution process (optionally including activation). These examplesmay be combined with features of activating and/or depositing asdescribed above.

Example A: Substitution may comprise HF/MSA activation and a platingprocess with an alkaline electrolyte that is depositing a 1-100 nm thickZnCr alloy layer. In addition or alternatively, an electrolyte can beused to apply a bare Zn layer.

Example B: Following an optional HF/MSA activation, a Cr-freeelectrolyte using an electrolyte of a bare zincate or zincate withvanadate or molybdate (instead of chromate, see Example A) may be used.

Example C: A dip process in each of the electrolytes mentioned inExample A and Example B can be performed for substituting. A dip is ashort (e.g. 1 to 120 s) exposure of the aluminum oxide surface with therespective electrolyte used, one of the Following an optional HF/MSAactivation, a Cr-solution without application of a current. During thedip, the aluminum oxide is substituted by the respective Zn or Zn alloylayer.

Example D: A plasma process (such as, e.g., described above) withincorporation of the substituting metal into the aluminum oxide layercan be used. To this end, a metalorganic molecule gas may be added tothe plasma and used as a source of the substitution metal to form the“soft substitute metal oxide”.

Example E: A sputtering process may be used to sputter the substitutemetal onto the Al₂O₃ layer in order to get a mixed oxide between Al₂O₃and the metal oxide, e.g. AlCu oxide or AlZn oxide.

Referring to FIG. 1D, the substitute metal or substitute metal alloyoxide layer 130 is at least partly reduced. A first possibility to atleast partly reduce this layer is to apply a reducing gas at elevatedtemperature for reducing the substitute oxides (e.g. ZnO and/orZnCr-oxide and/or ZnMo-oxide and/or ZnV-oxide, etc.) of the substitutemetal or substitute metal alloy oxide layer 130. The application of areducing gas is indicated in FIG. 1D by arrows Rg.

When applying a reducing gas, according to a first example a so-calledforming gas comprising a mixture of H₂ and an inert gas such as, e.g.,N₂, may be used as a reducing gas. In the following, without loss ofgenerality, N₂ is taken as an example of the inert gas.

A forming gas N₂/H₂ may have a concentration of H₂ in the range of0.001% to 10%. In particular, a N₂/5% H₂ forming gas may be used.

The elevated temperature of the reducing gas, when applied to thesubstitute metal or substitute metal alloy oxide layer 130, may be in arange between 150° C. and 500° C. More specifically, the elevatedtemperature of the reducing gas Rg may be equal to or less than orgreater than 500° C., 450° C., 400° C., 380° C., 350° C., 330° C., 300°C., 270° C., 250° C., 220° C., or 200° C. In particular, a temperatureof 330° C. ±30° C. may be used.

The pressure of the reducing gas Rg may be in a range between 10⁻⁵ Paand 10⁷ Pa. In particular, a pressure of about 10⁻³ Pa within a marginof, e.g., 10⁻⁴ Pa to 10⁻² Pa may be used. By way of example, ZnO isreduced from N₂/5% H₂ already at a temperature of 330° C. at a pressureof 10⁻³ Pa.

According to a second example, the reducing gas Rg may comprise amixture of an inert gas (e.g. N₂) and CH₂O₂ (formic acid). CH₂O₂ may beused in a concentration in the range between 0.01% and 10% in the inertgas. In particular, a concentration of 3% formic acid in N₂ may be used.

A reducing gas Rg of N₂/CH₂O₂ may be applied at temperatures in the samerange or even below the temperatures mentioned for the application of aN₂/H₂ forming gas. The applied pressure of N₂/CH₂O₂ reducing gas Rg maybe in the same range as mentioned for the N₂/H₂ forming gas. By way ofexample, ZnO is reduced from N₂/CH₂O₂ even at lower temperatures ofequal to or less than 250° C. at a pressure of 10⁻³ Pa.

It is also possible to apply a mixture of the above-mentioned reducinggases Rg (i.e. a mixture of H₂ and CH₂O₂ in an inert gas) within thesame temperature and/or pressure ranges as mentioned above.

Other reducing gases which may be applied are ethanol, acetone,propanol, ethene and homologues, ethyne and homologues or other volatileagents that can form active (reductive) hydrogen on the surface leadingto the formation of, e.g., a bare metal surface. For these otherreducing gases, the same ranges of pressure and/or temperature apply asmentioned above.

The application of a reducing gas Rg for reducing the substitute metaloxide or substitute metal alloy oxide in the substitute metal orsubstitute metal alloy oxide layer 130 may optionally be enhances by theapplication of an RF (radio frequency) plasma or a microwave plasma(MW). For instance, reductive gases or radicals can also come fromplasma treatment of the less stable metal oxides with H₂ or H-containinggases (e.g. CHF₃, CH₂F₂, CH₃F, CH₄, etc., or gas mixtures thereof) inchemical or in RF plasmas.

More specifically, FIG. 2 illustrates calculated equilibrium pressures pin units of Pa of H₂O for various metal oxides in the two reducing gasesRg mentioned above versus temperature in units of K. The equilibriumreactions in the forming gas of H₂ in N₂ areAl₂O₃+3H₂⇔2Al+3H₂OCr₂O₃+3H₂⇔2Cr+3H₂OZnO+H₂⇔Zn+H₂O  (1)and the equilibrium reaction in the reducing gas of CH₂O₂ in N₂ isAl₂O₃+3CH₂O₂⇔2Al+3H₂O+3CO₂.  (2)

From FIG. 2 it is apparent that the reduction of ZnO and Cr₂O₃ in N₂/H₂is possible at significantly lower temperature than the reduction ofAl₂O₃ in N₂/H₂, i.e. the thermodynamic stability of the aforementionedsubstitute metal oxides is significantly smaller than the thermodynamicstability of aluminum oxide. Further, FIG. 2 illustrates that CH₂O₂ ismore effective in reducing aluminum oxide than H₂. Although the higherefficiency of CH₂O₂ is illustrated in FIG. 2 only for aluminum oxide, italso holds true for the reduction of the substitute metal oxides (i.e.ZnO and/or Cr₂O₃, etc.). Further, FIG. 2 illustrates that the reductionof the substitute metal oxide(s) is already possible at temperatureswhich can readily be applied during semiconductor processing.

Referring to FIG. 1E, reduction of the substitute metal oxide(s) in thesubstitute metal or substitute metal alloy oxide layer 130 generates the(oxide-reduced) substitute metal or substitute metal alloy layer 140.This (oxide-reduced) substitute metal or substitute metal alloy layer140 will no longer contain ZnO and/or other oxides of the substitutemetal(s). As will be described further below, the reduction by, e.g.,usage of a reducing gas Rg may enable soldering of the aluminummetallization 110 without the usage of highly activating fluxes or evenwithout the usage of any fluxes. In addition, this enables soldering ofthe aluminum metallization 110 in general with a minimum influence ofcorrosive attack during the activation/substitution treatment as theactivation of the aluminum via dissolution of the Al₂O₃ is occurringduring, e.g., electrochemical deposition of the substitution metal (e.g.Zn or Zn-alloy). The attack and substitution of the Al₂O₃ with the “softmetal oxide” is in this case additionally supported by the depositioncurrent at the cathode.

FIGS. 1F to 1I illustrate stages of an exemplary process of soldering aconductor 150 to the aluminum metallization 110 when covered by an(oxide-reduced) substitute metal or substitute metal alloy layer 140 asproduced, e.g., by the reduction process of FIG. 1D.

According to FIG. 1F, a solder deposit 160 is disposed over the aluminummetallization 110. More specifically, the solder deposit 160 is appliedto the (oxide-reduced) substitute metal or metal alloy layer 140.

The application of the solder deposit 160 may be performed by standardsolder attach processes. The solder deposit 160 comprises a soldermaterial and may comprise a flux. The solder material may, e.g., containPb. By way of example, a PbSnAg solder may be used. By way of example, a95.5Pb-2Sn-2.5Ag solder (i.e. a solder having a composition of 95.5% wtof Pb, 2% wt of Sn and 2.5% wt of Ag) or a SnAgCu solder or a Sb—Snsolder or any other standard solder conventionally used forsemiconductor chip soldering can be used.

The soldering to the aluminum metallization 110 is done with metalscontained as a contribution in the solder material that are reactingwith aluminum by forming intermetallic phases. Metals that undergo areaction with aluminum are, e.g., Cu, Ni, Ti, V, Zn, Fe, Ta, and/or W(Sn, however, does not undergo a reaction with aluminum). These metals(i.e. the metal(s) that form(s) an intermetallic phase(s) with aluminum)may be provided by various ways:

According to one possibility this or these metal(s) may be contained asa contribution in the material of the conductor 150 (i.e. the solderingpartner), e.g. a clip. According to another possibility, the metal(s)may be alloyed in the solder material as a mixture. Further, it ispossible that the metal(s) are provided by metal particles in the soldermaterial. The metal(s) can further be provided via plating the metalsonto a solder-wire or by providing the metal(s) in the form ofmetalorganic molecules as a part of the flux.

The above mentioned possibilities of how to apply the metal(s) for theintermetallic phase(s) may be combined. By way of example, thecomposition of the solder material may contain a contribution of a metalwhich forms or is included in the conductor 150. If the conductor 150has a surface facing the solder deposit 160 which comprises or is of,e.g., Cu, Ni, Cu/Ni, NiP, Ni/NiP or alloys thereof, the solder materialmay also contain a contribution of Cu, Ni, Cu/Ni, NiP, Ni/NiP or alloysthereof.

As a further example, a 95.5Pb-2Sn-2.5Ag solder and a conductor 150(e.g. clip) consisting of Cu and a Cu—Fe—P alloy was used.

Standard lowly activating flux (which is not overly corrosive) or nofluxes may be used in the soldering process. In particular, no highlyactivating fluxes such as fluxes destined for Al₂O₃ reduction need to beused. Rather, the activation of the aluminum metallization 110 bydissolution of the aluminum oxide layer 120 was accomplished during theelectrochemical or electroless deposition of the substitute metal orsubstitute metal alloy on the aluminum oxide layer 120, see FIG. 1B.This substitute metal or substitute metal alloy deposition activationhas a minimum impact of corrosive attack and therefore enables solderingon the aluminum metallization 110 in semiconductor device manufacturingas considered herein.

The application of the solder deposit 160 may be performed in a vacuumsoldering furnace (not shown). For example, the solder deposit 160 maybe dispensed in form of a solder paste over the aluminum metallization110.

It is to be noted that application of the solder deposit 160 (see FIG.1F) and the aforementioned process of reducing the substitute metaloxide(s) may be accomplished in one and the same soldering furnace. Inparticular, the soldering process may be performed in the reducing gasRg atmosphere used for the oxide reduction process. In general, whenusing a reducing gas Rg, the process of at least partly or completelyreducing the substitute metal oxide(s) in the substitute metal oxide orsubstitute metal alloy oxide layer 130 may be performed prior to orduring the process of soldering the conductor to the aluminummetallization 110.

FIG. 1G illustrates the placement of the conductor 150 to the liquidsolder deposit 160. The solder deposit 160 may then cool to, e.g., 50°C. to 80° C. and solidifies during this process (FIG. 1H).

FIG. 1I illustrates an arrangement 100 comprising the conductor 150bonded to the aluminum metallization 110 by a solidified solder layer160′. The solidified solder layer 160′ may directly contact the(oxide-reduced) substitute metal or substitute metal alloy layer 140.That way, the conductor 150 is mechanically fixed and electricallyconnected to aluminum metallization 110.

According to a second possibility to at least partly reduce thesubstitute metal or substitute metal alloy oxide layer 130, the processof reducing the substitute metal oxide(s) by the application of areducing gas Rg (FIG. 1D) may be omitted. Rather, the reduction of thesubstitute metal oxide(s) may be performed during the subsequentsoldering process. This process will exemplarily be described below withreference to FIGS. 3A to 3D.

In this case, according to FIG. 3A, the solder deposit 160 is applied tothe aluminum metallization 110. More specifically, however, the solderdeposit 160 is applied to the substitute metal or substitute metal alloyoxide layer 130 (of FIG. 1C) rather than to the (oxide-reduced)substitute metal or substitute metal alloy layer 140 of FIG. 1E. Thatis, no substitute metal or substitute metal alloy oxide reduction (FIG.1D) has been performed.

The application of the solder deposit 160 may be performed by standardsolder attach processes. The solder deposit 160 comprises a soldermaterial and may comprise a flux. The solder material may, e.g., containPb. In particular, the same PbSnAg solder as mentioned above inconjunction with FIG. 1F could be used.

By way of example, a 95.5Pb-2Sn-2.5Ag solder (i.e. a solder having acomposition of 95.5% wt of Pb, 2% wt of Sn and 2.5% wt of Ag) or aSnAgCu solder or a Sb—Sn solder or any other standard solder andstandard low activated flux conventionally used for semiconductor chipsoldering can be used. Usual fluxes used in semiconductor solderingwhich can also be used here are low activated and based on colophony(rosin) or other organic acids such as malonic acid or oxalic acid.Soldering can also be done as a solder-wire or solder-preform basedsolder process with either flux or in reductive atmosphere.

Further, the same compositions of the solder material and/orcompositions of the conductor 150 as mentioned above in the context ofintermetallic phase formation can be used. The solder material maycontain a contribution of a metal which forms or is contained in theconductor 150. Reference is made to the corresponding disclosure above.

The application of the solder deposit 160 may be performed in a vacuumsoldering furnace (not shown). For example, the solder deposit 160 maybe dispensed in form of a solder paste over the aluminum metallization110.

Standard lowly activating fluxes for semiconductor device soldering(i.e. fluxes which are not overly corrosive) may be used in thesoldering process. In particular, no highly activating fluxes need to beused. As already described above and referred to in this context, theactivation of the aluminum metallization 110 by dissolution of thealuminum oxide layer 120 has been performed during preceding processing(i.e. was caused during the electrochemical or electroless deposition ofthe substitute metal or substitute metal alloy on the aluminum oxidelayer 120, see FIG. 1B).

The substitute metal oxide(s) (e.g. ZnO and/or Cr₂O₃, etc.) are reducedby direct contact of the solder deposit 160 with the substitute metal orsubstitute metal alloy oxide layer 130. More specifically, an(oxide-reduced) substitute metal or substitute metal alloy layer region140_1 having, e.g., the same composition as the (oxide-reduced)substitute metal or substitute metal alloy layer 140 of FIG. 1E isgenerated from the substitute metal or substitute metal alloy oxidelayer 130 in a region where the solder deposit 160 contacts or overlapsthe substitute metal or substitute metal alloy oxide layer 130.Laterally outside the overlapping region, the substitute metal oxides ofthe substitute metal or substitute metal alloy oxide layer 130 are notreduced, i.e. the (oxide-reduced) substitute metal or substitute metalalloy layer region 140_1 may be surrounded by an unchanged region 130_1of the substitute metal or substitute metal alloy oxide layer 130 (FIG.3B).

FIG. 3B further illustrates the placement of the conductor 150 to theliquid solder deposit 160. The solder deposit 160 may then cool to,e.g., 50° C. to 80° C. and solidifies during this process as describedin conjunction with FIG. 1H.

FIGS. 3C and 3D correspond to FIGS. 1H and 1I, respectively, andreference is made to the description above to avoid reiteration. Withthe conductor 150 being mechanically fixed and electrically connected tothe aluminum metallization 110 by the solidified solder layer 160′, thedifference between the processes shown in FIGS. 1D to 1I (overall oxidereduction by applying a reducing gas Rg) and FIGS. 3A to 3D (localizedoxide reduction by contacting with the solder deposit 160) remaindetectable in the finalized arrangement 300 by the provision of theunchanged region 130_1 of the substitute metal or substitute metal alloyoxide layer 130. That is, the (oxide-reduced) substitute metal orsubstitute metal alloy layer region 140_1 is confined to a region of thesame shape as the solidified solder layer 160′ and surrounded by theunchanged region 130_1 of the substitute metal oxide or substitute metalalloy oxide layer. The solidified solder layer 160′ may directly contactthe (oxide-reduced) substitute metal or substitute metal alloy layerregion 140_1.

According to a second aspect of the disclosure, as illustrated by way ofexamples in FIGS. 4A to 4D, no conditioning or activation of thealuminum oxide layer 120 on the aluminum metallization 110 is required.Instead, removal of the aluminum oxide may be reached by applying a fluxmaterial to the aluminum oxide layer 120 on the aluminum metallization110 and by disposing a solder material over the aluminum metallization,wherein the solder material has a substantial content of Zn. Morespecifically, the chemical composition of the solder material may be x %wt≤Zn≤100% wt, with x=10, 30, 50, 70, 90, 95 or 100.

The rest of the chemical composition of the solder material may containone or more of Al, Cu, Ni, Ti and, optionally, residual components asmentioned above. In particular, a solder material consisting mainly orexclusively of Zn and Al (i.e. ZnAl or AlZn or an alloy thereof with theabove composition) may be used. The higher the Zn content, the moreeffective is the solder material in removing the aluminum oxide from thealuminum metallization, i.e. in reducing the aluminum oxide duringsoldering together with the flux material.

In order to prevent any halogenide-catalyzed corrosion, other moleculesare added to dissolve the Al₂O₃ effectively. A first possibility is toadd silicates, e.g. specific silicates such as zeolites to the fluxmaterial. By way of example, silicates (or zeolites) in theconcentration range of 0.01% wt to 10% wt in relation to the fluxcontent may be added. Silicates (or zeolites) are effective indecreasing the corrosive impact of the flux material.

For example, the flux material may be a mixture of at least flux andsilicate (zeolite), the flux material having a chemical composition of x% wt≤silicate and/or silicate≤x % wt, with x=0.1, 0.5, 1.0, 2.0, 4.0,6.0, or 8.0. The rest of the chemical composition of the flux materialmay be a (highly activated) flux capable of reducing Al₂O₃.

A further possibility to decrease the corrosive impact via halogenidesis the addition of crown ether to the flux. By way of example, crownether in the concentration range of 0.01% wt to 50% wt in relation tothe flux content may be added. By way of example, the flux material maybe a mixture of at least flux and crown ether, the flux material havinga chemical composition of x % wt≤crown ether and/or crown ether≤x % wt,with x=0.1, 0.5, 1, 5, 10, 20, 30, or 40. The rest of the chemicalcomposition of the flux material may be a (highly activated) fluxcapable of reducing Al₂O₃.

Both measures of reducing the corrosive impact of the flux material(i.e. the addition of silicates (e.g. zeolites) and the addition ofcrown ethers to flux) may be combined. Silicates (e.g. zeolites) and/orcrown ethers may be helpful to minimize corrosion as they may catchanions and cations during and after the soldering process. Further,besides silicates and crown ether, other aluminum complexing agents maybe added to the flux in the concentration range of 0.01% wt to 10% wt inrelation to the flux content.

The reduction of the corrosive impact of the flux material by, e.g., oneor more of the above measures allows to use highly activating fluxes inthe flux material for semiconductor device soldering.

Referring to FIG. 4A, a solder paste 460 is applied over the aluminummetallization 110. The aluminum metallization 110 still comprises thealuminum oxide layer 120. The same application/dispensing processes asdescribed in conjunction with FIG. 1F may be applied. The flux materialand the solder material may, e.g., already be mixed together beforeapplication to form the solder paste 460. The solder material may have acomposition as stated above and the flux material may have a compositionas stated above.

During or after application the solder paste 460 is heated and theconductor 150 is placed on the solder paste 460 (FIG. 4B). Similarprocesses as described in conjunction with FIGS. 3A and 3B may beapplied, and reference is made to the above disclosure. In particular,the soldering process may be supported by the application of a reducinggas and/or by the application of an RF-plasma as described inconjunction with FIGS. 1D to 1G. As described above, placement of theconductor 150 (FIG. 4B) and soldering (FIG. 4C) may, e.g., be performedin a tunnel furnace (not shown).

Still referring to FIG. 4B, the aluminum oxide of the aluminum oxidelayer 120 is reduced by direct contact of the solder paste 460 with thealuminum oxide layer 120. More specifically, an (oxide-reduced) aluminumregion 420_1 is generated from the aluminum oxide layer 120 in a regionwhere the solder paste 460 contacts or overlaps the aluminum oxide layer120. Laterally outside the overlapping region, the aluminum oxide layer120 is not reduced, i.e. the (oxide-reduced) aluminum region 420_1 maybe surrounded by an unchanged region 120_1 of the aluminum oxide layer120 (FIG. 4B).

The aluminum metallization 110 may consist of bare aluminum or analuminum alloy as described above. In particular, an aluminum alloy98.5Al-0.5Cu-1Si or 99Al-1Si front side metallization may be used. Theconductor 150 to be soldered to the aluminum metallization 110 maycomprise or be of the same materials as mentioned above, e.g. of Cu, Ni,Cu/Ni, NiP, Ni/NiP or alloys thereof. These substances refer to thecomposition of the surface region of the conductor 150 which effectivelyprovides the material that contributes to the intermetallic compoundgenerated during soldering. The intermetallic compound is generatedduring soldering by the reaction of the solder material with the surfaceregion of the conductor and the aluminum metallization 110 (or, morespecifically, the (oxide-reduced) aluminum region 420_1).

Then, the solder paste 460 is cooled to solidify and to provide for amechanical and electrical connection. Reference is made to thedescription of FIGS. 1H, 1I and 3C, 3D, which may be identically appliedto the processes illustrated by FIGS. 4C and 4D, respectively, with theexception that no intermediate (oxide-reduced) substitute metal orsubstitute metal alloy layer 140 (see FIGS. 1H, 1I) or (oxide-reduced)substitute metal or substitute metal alloy layer region 140_1 (FIGS. 3C,3D) is provided between the solidified solder paste 460′ and thealuminum metallization 110. Rather, the solidified solder paste 460′ maydirectly connect to the aluminum metallization 110 (via the(oxide-reduced) aluminum region 420_1 of a thickness of only a few nm).

FIG. 4D is a cross-sectional view illustrating an example of anarrangement 400 comprising the conductor 150 soldered to the aluminummetallization 110 by exemplary processes as illustrated, e.g., in FIG.1A, followed by exemplary processes as illustrated, e.g., in FIGS. 4A to4C.

FIGS. 5A to 5F illustrate stages of various embodiments of a method ofsoldering a conductor to an aluminum metallization according to a thirdaspect of the disclosure. According to a third aspect of the disclosure,no conversion of the Al₂O₃ layer by a process of substituting thealuminum by another metal or metal alloy as described for the firstaspect of the disclosure is needed.

Referring to FIG. 5A, an aluminum metallization 110 is covered by analuminum oxide layer 120. Reference is made to the description of FIG.1A to avoid reiteration.

FIG. 5B schematically illustrates several examples for activating thealuminum oxide layer 120. Activating the aluminum oxide layer 120 mayhave the meaning of decreasing the stability of the aluminum oxide layer120. Here, the activation of the aluminum oxide layer 120 is performedby applying a halogenide via a plasma process to the aluminum oxidelayer 120 on the aluminum metallization 110 to produce a halogenatedaluminum oxide layer 540 (see FIG. 5C). That is, the activation (AC) ofthe aluminum oxide layer 120 for decreasing its stability may beachieved by the incorporation of halogenides, e.g. one or more of F, Cl,Br, and J.

Several possibilities are available and may, e.g., be combined ifdesired:

(1) Plasma treatment of Al₂O₃ with fluorocarbon containing plasmas suchas, e.g., CHF₃, C₂F₂, CH₃F or CF₄ gases or gas mixtures, e.g. also mixedwith one or more of Ar, He, O₂, H₂ or H₂O. Again, F may be substitutedby other halogenides.

(2) Plasma treatment of Al₂O₃ with other fluorine or chlorine compoundplasmas such as, e.g., SF₆, CHCl₃, CH₂Cl₂, CH₃Cl, CCl₃.

(3) Plasma treatment of Al₂O₃ with brominated or iodized organicmolecules that leads to incorporation of these halogens into the Al₂O₃layer leading to a weakening of this layer.

During the plasma treatment of the Al₂O₃ with a halogenide-based plasmaa specific mixture of aluminum-oxyfluorides are forming which are lessstable and can be soldered with standard flux-solderpastes or even asolderwire. Standard flux-solderpastes can be solderpastes containingfluxes which are usually used in semiconductor soldering, such as lowactivated fluxes based on kolophonium or other organic acids such asmalonic acid or oxalic acid.

As already mentioned, usual contents of halogenides (e.g.fluorine-based) in the Al₂O₃ layer may be measured with Auger depthprofiles. Taking fluorine as an example, a F/O atomic concentrationratio of, e.g., about 0.5 is observed at the F maximum peak over sputtertime. Atomic concentration ratios at the maximum F content (or, ingeneral, halogens content) along the Al₂O₃ layer thickness between 0.01and 10 have been observed and may be suitable for soldering of aluminumdue to the weakened Al₂O₃ layer.

In contrast to the (optional) activation as describe in conjunction withFIG. 1B, according to the third aspect of the disclosure the treatment(activation) of the Al₂O₃ with a halogenide-based plasma is used as a“stand alone” process. “Stand alone” here means that no conversion ofthe Al₂O₃ layer by a process of substituting the aluminum by anothermetal or metal alloy is used. Rather, the halogenated aluminum oxidelayer 540 (i.e. the Al₂O₃ layer with the incorporated halogen) isdirectly soldered.

FIGS. 5C to 5F illustrate stages of an exemplary process of soldering aconductor 150 to the aluminum metallization 110 to manufacture anarrangement 500. Except the replacement of the (oxide-reduced)substitute metal or substitute metal alloy layer 140 by the halogenatedaluminum oxide layer 540, FIGS. 5C to 5F correspond to FIGS. 1F to 1I,respectively, and reference is made to the above description to avoidreiteration.

Generally, soldering can be done on aluminum chip metallizations (chipelectrodes) and/or on aluminum conductors such as, e.g., chip carriersand/or clips. FIG. 6 illustrates an exemplary arrangement 600 of aconductor 150 and an aluminum metallization 110 soldered together. Inthis example, the aluminum metallization 110 is formed by a firstelectrode 611 of a semiconductor chip 610 and the conductor 150 isformed by a chip carrier 620, e.g. a leadframe. The semiconductor chip610 may, e.g., be a power device having, e.g., a vertical structure. Thefirst electrode 611 of the semiconductor chip 610 may, e.g., either be adrain electrode (drain-down orientation) of the semiconductor chip 610or a source electrode (source-down orientation) of the semiconductorchip 610.

Further referring to FIG. 6, the conductor 150 to be soldered to thealuminum metallization 110 may be a clip 630 and the aluminummetallization 110 may again be a chip electrode, e.g. a second chipelectrode 612. The second chip electrode 612 may be a source electrode(drain-down orientation) or a drain electrode (source-down orientation)of the semiconductor chip 610.

Chip carrier 620 (150) soldering and/or clip 630 (150) soldering of thesemiconductor chip 610 may be accomplished subsequently orsimultaneously. Any of the above mentioned processes, materials,techniques etc. may be applied. In particular, all arrangements 100,300, 400, 500 described above for soldering of a conductor 150 to analuminum metallization 110 may be applied in the arrangement 500 forchip carrier 620 (150) soldering and/or clip 630 (150) soldering of theelectrodes 611 (110) and/or 612 (110) of the semiconductor chip 610.

According to a further possibility depicted in FIG. 7, an exemplaryarrangement 700 may include chip electrodes 611 and/or 612 whichrepresent the conductor 150 and are made of, e.g., one or more of theabove mentioned materials of the conductor 150. In this case, the chipcarrier 620 such as, e.g., a leadframe provides for the aluminummetallization 110 and/or the clip 630 provides for the aluminummetallization 110. Again, source-down or drain-down orientations arepossible and both semiconductor electrodes 611 and 512 may be solderedsubsequently or simultaneously to the chip carrier 620 (110) and to theclip 630 (110). In particular, all arrangements 100, 300, 400, 500described above for soldering of a conductor 150 to an aluminummetallization 110 may be applied in the arrangement 700 for chip carrier620 (110) soldering and/or clip 630 (110) soldering of the electrodes611 (150) and/or 612 (150) of the semiconductor chip 610.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat a variety of alternate and/or equivalent implementations may besubstituted for the specific embodiments shown and described withoutdeparting from the scope of disclosure. This application is intended tocover any adaptations or variations of the specific embodimentsdiscussed herein.

What is claimed is:
 1. A method of soldering a conductor to an aluminummetallization, the method comprising: substituting an aluminum oxidelayer on the aluminum metallization by a substitute metal oxide layer ora substitute metal alloy oxide layer; removing metal oxides from thesubstitute metal oxide layer or substitute metal alloy oxide layer byapplying a flux material to the substitute metal oxide layer or to thesubstitute metal alloy oxide layer to generate a reduced substitutemetal layer or substitute metal alloy layer; and soldering the conductorto the aluminum metallization via the reduced substitute metal layer orreduced substitute metal alloy layer using a solder material.
 2. Themethod of claim 1, wherein a substitute metal of the substitute metaloxide layer is one of Zn, Cr, Cu, Pb, or Sn.
 3. The method of claim 2,wherein substituting comprises depositing the substitute metal over thealuminum oxide layer by an electrochemical deposition process.
 4. Themethod of claim 2, wherein substituting comprises depositing thesubstitute metal over the aluminum oxide layer by an electrolessdeposition process.
 5. The method of claim 1, wherein a substitute metalalloy of the substitute metal alloy oxide layer comprises at least twoof the elements Zn, Cr, V, Cu, Pb, Sn, and Mo.
 6. The method of claim 5,wherein substituting comprises depositing the substitute metal alloyover the aluminum oxide layer by an electrochemical deposition process.7. The method of claim 5, wherein substituting comprises depositing thesubstitute metal alloy over the aluminum oxide layer by an electrolessdeposition process.
 8. The method of claim 1, wherein substitutingcomprises applying one or more of hydrofluoric acid (HF) andmethanesulfonic acid (MSA) to the aluminum oxide layer.
 9. The method ofclaim 1, wherein substituting comprises applying a halogenide via aplasma process to the aluminum oxide layer.
 10. The method of claim 1,wherein the flux material comprises a lowly activating flux.
 11. Themethod of claim 1, wherein the solder material comprises one of PbSnAg,SnAgCu, or Sb—Sn.
 12. The method of claim 1, wherein the solder materialcomprises at least one of Cu, Ni, Ti, V, Zn, Fe, Ta, and W.
 13. A methodof soldering a conductor to an aluminum metallization, the methodcomprising: substituting an aluminum oxide layer on the aluminummetallization by a substitute metal oxide layer or a substitute metalalloy oxide layer; applying a flux material to the substitute metaloxide layer or to the substitute metal alloy oxide layer; and solderingthe conductor to the aluminum metallization using a solder material,wherein the flux material is applied during soldering the conductor tothe aluminum metallization.
 14. A method of soldering a conductor to analuminum metallization, the method comprising: substituting an aluminumoxide layer on the aluminum metallization by a substitute metal oxidelayer or a substitute metal alloy oxide layer; applying a flux materialto the substitute metal oxide layer or to the substitute metal alloyoxide layer to dissolve a substitute metal oxide in the substitute metaloxide layer or in the substitute metal alloy oxide layer to generate anoxide-reduced substitute metal or substitute metal alloy layer; andsoldering the conductor to the aluminum metallization via theoxide-reduced substitute metal or substitute metal alloy layer using asolder material.
 15. A method of soldering a conductor to an aluminummetallization, the method comprising: substituting an aluminum oxidelayer on the aluminum metallization by a substitute metal oxide layer ora substitute metal alloy oxide layer; applying a flux material to thesubstitute metal oxide layer or to the substitute metal alloy oxidelayer to dissolve a substitute metal oxide in the substitute metal oxidelayer or in the substitute metal alloy oxide layer; and soldering theconductor to the aluminum metallization using a solder material, whereinthe flux material is applied during soldering the conductor to thealuminum metallization.
 16. A method of soldering a conductor to analuminum metallization, the method comprising: substituting an aluminumoxide layer on the aluminum metallization by a ZnO layer; applying aflux material to the ZnO layer to generate an oxide-reduced Zn layerregion; and soldering the conductor to the aluminum metallization viathe oxide-reduced Zn layer region using a PbSnAg solder material. 17.The method of claim 16, wherein the flux material at least partlyreduces ZnO in the ZnO layer.
 18. The method of claim 16, wherein thePbSnAg solder material comprises 95.5Pb-2Sn-2.5Ag solder.
 19. The methodof claim 16, wherein the PbSnAg solder material comprises Cu.
 20. Amethod of soldering a conductor to an aluminum metallization, the methodcomprising: substituting an aluminum oxide layer on the aluminummetallization by a ZnO layer; applying a flux material to the ZnO layer;and soldering the conductor to the aluminum metallization using a PbSnAgsolder material, wherein the flux material is applied during solderingthe conductor to the aluminum metallization.